A technique for growing small P. maximus spat in suspension culture from rafts is described. Hatchery produced spat of initial size 3.0- and 4.3-mm shell height were transferred to a sea-based primary nursery system in May. Scallop spat (3.0 mm) grew to 16.8 ± 3.0 mm during 85 days. Survival was 70.0 ± 8.1%, but decreased due to presence of predators in 33.4% of the sampling units, to between 0 and 37.4%. Important predators were the crabs Atelecyclus undecimlineatus, Liocarcinus arcuatus, and Necora puber and the starfish Asterias rubens. A significant negative correlation was found between Asterias rubens arm length and survival of scallops. Initial shell height affected growth and survival significantly whereas stocking density (50–400 spat quarter−1 and initial coverage of 1% to 17%) had significant effect on growth. Spat of 4.3 mm initial size were significantly bigger than the spat of 3.0 mm after 34 and 57 days, whereas survival was 96.4 ± 4.4% versus 71.4 ± 12.8% after 37 days. No mortality occurred during the second sampling period, but growth was negatively correlated to increased density of spat. The results give important information regarding development of economic production of scallops and showed promising opportunities for optimizing stocking density in intermediate primary culture. The choice of production methods in the next production step (secondary nursery stage) can be based on the results obtained.
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Vol. 24 • No. 1